This invention relates to an admixture for cements or cement mixes, and more particularly to a cement admixture which can prevent the lowering with time of the fluidity of concrete, mortar, or paste which is a hydraulic cement mix and improve its applicability and workability.
Conventionally, a cement mix prepared by mixing cement with water and, if necessary, sand, gravel, and admixtures loses its fluidity gradually after mixing, and its applicability and workability are lowered with the passing of time because the physical and chemical coagulation proceeds with the passing of time. Therefore, a cement mix has a drawback that its serviceable life (pot life) is limited. In most cases, cement mixes are transported to a concreting site by an agitator truck (a ready-mix concrete mixer truck) after they have been mixed in advance and the time necessary for transportion varies largely depending on the transportation distance and the extent of traffic jams. Therefore, it is extremely difficult to achieve constant applicability at the concreting site because the fluidity of the concrete varies with each agitator truck.
Further, there are many problems in pumping a cement mix in that when the pumping is discontinued for the sake of a lunch break or a change in the work procedures and the pumping is restarted, the fluidity of the concrete mix in the pipe is lowered and the pumping pressure rises suddenly upon restarting the pumping or blockage occurs.
Further, in performing centrifugal compaction of concrete or mortar, concrete is placed in a centrifugal molding form after mixing and the centrifugal compaction is performed usually after several molding forms have been filled. In these cases, if a long time is required to fill the forms, the concrete loses its fluidity and becomes difficult to compact centrifugally.
Therefore, several processes have been proposed for preventing the fluidity loss of a cement mix.
For example, a process was proposed in which a retarder such as a hydroxycarboxylic acid was added for the purpose of preventing chemical coagulation. According to this process, it is difficult to prevent physical coagulation, though the hydration reaction of cement can be retarded, so that the slump loss can not be sufficiently prevented. Further, it has a drawback that the early strength of concrete or mortar is lowered.
Another process was proposed in Japanese Patent Laid-Open No. 139929/1979 in which the slump loss could be prevented by adding a granular concrete fluidizer such as .beta.-NSF to concrete or the like and gradually dissolving the fluidizer. According to this process, it is possible to prevent the slump loss to some extent, but it has a drawback that the strength and durability are lowered because the granular fluidizer remains locally in the hardened concrete.
According to still another process disclosed in Japanese Patent Publication No. 15856/1976 the fluidity of concrete can be maintained for a long time by adding a fluidizer such as .beta.-NSF in divided portions or continuously to concrete or the like. Although this process is effective as a process for preventing the slump loss, the addition of the fluidizer in this manner is laborious, and it is impossible to prevent the slump loss of a concrete which is in a state in which the divided addition of a fluidizer is difficult, such as the one contained in piping for pumping, or the one contained in a centrifugal compaction form.
Thus, each of these conventional processes for preventing the fluidity loss of a cement mix has several problems so that they can not be thought to be satisfactory.